The invention is directed toward catheters having an elongated flexible catheter member and a short rigid catheter tip. Catheter members are typically about 0.5 m to 1.5 m long depending on its intended clinical application. Rigid catheter tips are typically about 0.3 cm to 1.5 cm long. The catheter members and the catheter tips have a 1.65 mm to 3.3 mm outside diameter corresponding to French Gauge 5-10. Catheter tips terminate in a leading catheter dome typically formed from bio-compatible materials such as platinum, iridium, and the like. For certain surgical procedures, catheter tips are intended to be introduced into a human lumen via an externally accessible access port to be steered therealong to a therapy site for therapy thereat before being pulled back along the human lumen to leave therefrom at the access port in a single clinical procedure. In greater particularity, the present invention is directed towards cryocatheters for cryotherapy at a therapy site at cryo-temperatures which in the context of the present invention are sub-zero tip temperatures of −10° C. and colder.
Cryocatheters are presently implemented employing the Joule-Thomson effect, namely, passing a liquid, gas or vapor refrigerant through a pressure line at 70 bar to 150 bar to exit through a restriction at a catheter tip. The restriction causes a phase change from, say, liquid to vapor, to cause a loss of pressure with consequent loss of heat and rapid cooling to freeze a catheter tip to a cryo-temperature. Exemplary prior art patent publications include inter alia U.S. Pat. No. 5,807,391 to Wijkamp entitled CryoAblation Catheter, US Patent Application Publication No. 2011/0196359 entitled Catheter with Cryogenic and Electrical Heating Ablation, PCT International Publication No. WO 2010/121739 entitled Cryosurgical Instrument particularly suitable for transbronchial biopsy, and the like.
Cryocatheters are commercially available from Medtronic CryoCath, Inc. www.cryocath.com under several trade names including inter alia FREEZOR® MAX Cardiac CryoAblation Catheter, and ARCTIC FRONT® Cardiac CryoAblation Catheter. The cryocatheters employ nitrous oxide or argon refrigerant and are capable of heat transfer of several dozens of watts of thermal energy from human tissue over a period of 4 to 5 minutes for freezing a catheter tip to as low as −150° C. to create a so-called ice ball of up to a size of 20 mm diameter for high cryoenergy purposes, for example, cryoablation, and the like. The cryocatheters are also operated at partial cryocapacities for low and mid cryoenergy purposes, for example, ice mapping procedures at a typically narrow temperature range of −10° C. to −20° C., and the like. The cryocatheters are considered to be less steerable than their non-cryo counterparts because of their construction to withstand high pressure which can lead to greater difficulty to steer them to a desired therapy site. Moreover, the cryocatheters have a relatively large cryotemperature stability range of about +/−10° C. and are highly expensive.
Stroke hemorrhages are an acute neurologic injury occurring as a result of bleeding into the brain. There are two distinct mechanisms: bleeding directly into the brain parenchyma known as IntraCerebral Hemorrhage hereinafter referred to as ICH, or bleeding into the CerebroSpinal Fluid (CSF) between the brain and the skull known as SubArachnoid Hemorrhage hereinafter referred to as SAH. In most of cases, it results from a weakened vessel that ruptures and bleeds into the surrounding brain such as the Middle Cerebral Artery (MCA) area. Blood accumulates and compresses the surrounding brain tissue which may lead to severe damage of the tissue, permanent brain injury or even a death. According to the World Health Organization, approximately 30 million people had a stroke in the year 2000. 15% of patients were diagnosed with stroke hemorrhages (4.5 million people).
Treatment depends substantially on the type of a stroke and includes both medication and surgery. Main medications include antihypertensive drugs such as beta blockers and blood coagulators. Surgery procedures include, for example, craniotomy, namely, cutting a hole in the skull, and aneurysm clipping. This is suitable only for SAH in the areas proximal to the skull. As of today, there isn't an effective minimal invasive procedure to close off a ruptured blood vessel in ICH cases.